#define   _CRT_SECURE_NO_WARNINGS 1
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
bool _isSymmetric(struct TreeNode* p, struct TreeNode* q)
{
    if (p == NULL && q == NULL)
        return true;
    if (p == NULL || q == NULL)
        return false;
    if (p->val == q->val)
        return _isSymmetric(p->left, q->right) && _isSymmetric(p->right, q->left); \
    else
        return false;
}
bool isSymmetric(struct TreeNode* root) {
    if (root == NULL)
        return true;
    return _isSymmetric(root->left, root->right);
}